1. Field of the Invention
The present invention relates to a control apparatus for an exhaust gas recirculation valve which is provided in an exhaust gas recirculation pipe for recirculating exhaust gases from an internal combustion engine to an intake system of the engine, and controls an exhaust gas recirculation amount.
2. Description of the Related Art
It is important for maintaining good exhaust characteristics to accurately and quickly control an opening of the exhaust gas recirculation valve which controls an exhaust gas recirculation amount of the internal combustion engine to a target opening. Therefore, Japanese Laid-open Patent Publication No. 2002-235606 shows a control apparatus in which an opening of the exhaust gas recirculation valve which is detected when the target opening is “0 (the fully-closed opening)” is learned as the fully-closed opening, the detected opening is corrected using the learned fully-closed opening, and the exhaust gas recirculation valve is controlled to the target opening according to the corrected detected opening.
According to the apparatus shown in the above publication, it is possible to maintain good control accuracy at a small opening even if there is aging in the opening characteristic of the exhaust gas recirculation valve. However, there is a problem described below when the exhaust gas recirculation valve is enlarged and the exhaust gas recirculation flow rate is controlled from a low flow rate to a high flow rate by only one large-size exhaust gas recirculation valve.
That is, good control accuracy at a very small opening (about 0.5 mm of the lift amount) is necessary for accurately controlling a low flow rate. However, good control accuracy in the small opening region of the large-size exhaust gas recirculation valve cannot be obtained.